Use of Fluorescence to Measure the Lubricant Excess Surface Density During Pool Boiling.
Use of Fluorescence to Measure the Lubricant Excess
Surface Density During Pool Boiling.
Kedzierski, M. A.
NISTIR 6727; 51 p. January 2001.
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fluorescence; lubricants; adsorption; refrigerants;
boiling; enhanced heat; pool boiling; R123; smooth
This paper presents what are believed to be the first
measurements of the non-adiabatic lubricant excess
surface density on a roughened, horizontal flat
pool-boiling surface. Both pool boiling heat transfer
data and lubricant excess surface density data are given
for pure R123 and a R123/lubricant mixture. A
spectrofluorometer was used to measure the lubricant
excess density that was established by the boiling of a
R123/lubricant mixture on a test surface. The
fluorescent measurement technique was used to confirm
the existence of the lubricant excess layer during
refrigerant/lubricant mixture boiling. The lubricant is
preferentially drawn out of the bulk
refrigerant/lubricant mixture by the boiling process and
accumulates on the surface in excess of the bulk
concentration. The excess lubricant resides in a very
thin layer on the surface and influences the boiling
performance. Accordingly, the ability to measure the
lubricant excess density on the heat transfer surface
would lead to a fundamental understanding of the
mechanism by which lubricants can degrade or improve
boiling performance. In support of this effort, heat
transfer data are provided for both pure R123 and an
R123/lubricant (98.2/1.8) by mass mixture at 277.6 K.
The heat transfer data shows that the lubricant excess
causes an average degradation of 12 % in the heat flux
for a given superheat.